"Go, Maddy!" Glinda, the Good Witch of the North, yelled from the orchestra pit.

Madeline "Maddy" Trumble, 13, smiled and nervously twisted her sandy hair into a long ponytail. Then, with a sudden jerk, she sailed straight up into the air and back into the shadows behind the main curtain at Walnut Creek's Dean Lesher Theater, her arms pulled close to her sides.

The instant her feet touched the ground Maddy skipped back to center stage, ready to fly again.

It doesn't take much to transform Maddy into Dorothy, the pig-tailed, wide-eyed, ruby-red-shoe wearing heroine in "The Wizard of Oz."

As Dorothy showed her bravery by standing up to the Wicked Witch of the West, Maddy, who recently entered her freshman year at Berkeley High School, shows hers by stepping out on stage before hundreds of people each night to portray the lead character in the Diablo Light Opera's production of the musical.

She will also perform in a cabaret showcase in San Francisco this weekend.

Maddy also is brave enough to follow her dream of being a performer despite suffering from juvenile diabetes, a potentially life-threatening condition.

More than 1 million Americans suffer from Type 1, or juvenile, diabetes, a condition in which the body loses its ability to make insulin, disrupting the metabolic system that turns food into biological fuel.

As their immune systems continue to malfunction, juvenile diabetics must continue receiving supplemental insulin doses in order to live.

When she was younger, Maddy would have to take blood tests and get insulin shots backstage during intermissions. In recent years, she's been able to wear a pump that constantly measures and regulates the level of insulin in her system.

But she'll probably have to remove the pump during the Wizard of Oz performances. That means Maddy will have to pay attention to how her body is feeling.

"Diabetes makes everything harder," Maddy admitted one afternoon before rehearsal. "The other day my blood sugar wasn't where it should have been, and I really couldn't get going."

The event caused some concern over Maddy's ability to be ready for opening night, but since then she hasn't had any further problems. Maddy, who learned she had the autoimmune deficiency on her first day of kindergarten, said she's used to having to keep track of her body.

"I don't remember what it used to be like when I didn't have (diabetes)," she said.

Maddy's mother, Barbara Weaver, believes the disease has made her daughter more conscientious.

"She's incredibly responsible," Weaver said. "And I think it makes you more mature."

Maddy was 7 years old when she performed her first show, "Annie Get Your Gun," at a small theater company in Alameda.

"I had so much fun that I haven't stopped since then," she said. "I just enjoy being on stage and having people get up and clap for you."

She recently won the youth division of a San Francisco cabaret competition at Herbst Theater. As her reward, she will get to belt out three tunes at the Plush Room in San Francisco this weekend.

Meanwhile, Diablo Light Opera will put on 19 "Oz" performances, through Sept. 27, at its 785-seat theater. The show will feature some of the most ambitious special effects sequences the company has ever attempted.

Following big brother

Maddy has been singing and dancing as long as she can remember. It started with wanting to emulate her older brother, Simon, who was also a performer.

"My son is sort of a natural performer," said Weaver. "So as soon as Madeline could walk she would perform with him in the living room."

Maddy's sister, Emily, 9, also has the performance bug, and is following in her siblings' dance steps. Weaver believes the children inherited their talent from their father, Ron, who once performed on Broadway in a production of "Children of a Lesser God."

"I do think they got the performing gene from him, because they sure didn't get it from me," Weaver said with a laugh.

"I'm excited that they found something that they love so much at an early age," Weaver said. "For some kids it's sports. My kids are just really into theater."

In a way, Maddy has been practicing all her life for the role of Dorothy. As a child she used to imagine herself in the role of the Kansas farm girl whisked away by a tornado to the magical land of Oz.

" 'The Wizard of Oz' was my favorite movie," Maddy said. "Since I was 2 or 3, I used to watch it every day."

From slippers to sneakers

Maddy used to collect pairs of red shoes and slippers and wear them whenever she watched the movie, but her taste in footwear has changed now that she's a teenager.

"If it were up to me I'd wear these," she said, looking down at her feet, which were clad in a pair of red canvas retro Chuck Taylor All-Stars sneakers.

But following in Judy Garland's footsteps isn't just about the shoes.

"For Dorothy, you have to have that sweet Kansas-like quality, or fake it.

But you also have to have like real emotions, like when Toto gets taken away, you have to be upset, cry," Maddy said. "I haven't watched the movie for a long time purposely, 'cause I didn't want to be doing it a certain way."

Producer Helene Harks said everyone in the production has been impressed with Maddy's effort.

"After her first audition, the director came to me and said, 'I had tears in my eyes listening to her sing,' " Harks said.

"I find her a typical little 13-year-old," Harks said, as she watched Maddy being fitted into her flying harness for the first time, "who is having a lot of fun."

She is also scheduled to sing in a cabaret showcase, starting at 7:30 p. m. Sunday at the Plush Room in the York Hotel, 940 Sutter St., San Francisco. Tickets cost $20, plus a two-drink minimum; for reservations, call (415) 885- 2800.